No child will be put into classrooms of a lesser standard if school merger and closure proposals go ahead, the Ministry of Education says.

But Christchurch principals are sceptical about the guarantee and do not believe the mergers and closures can be done effectively in just seven months.

Last week, Education Minister Hekia Parata announced plans to close seven schools and merge 12 to create six. Another 12 schools originally proposed for merger or closure will remain open.

Parata shocked principals by moving forward the date for the proposed closures and mergers to next year. Schools had previously been told they would have at least two years to plan for the changes.

Parata said the dates had been brought forward to provide certainty for pupils, parents, staff and the wider community.

Central New Brighton School principal Toni Burnside said she believed there was not enough time to merge Central at South New Brighton School.

It was important children from Central New Brighton felt they were part of something new and exciting rather than just feeling like they were add-ons at an existing school, she said.

The final decisions will not be confirmed until late May, leaving just six months for a new transitional board to be appointed, for that board to advertise and appoint a new principal and for staff to be employed, Burnside said.

New buildings would also have to be planned.

Phillipstown School principal Tony Simpson said he was left wondering when children were going to get the 21st century modern buildings Parata kept promising.

He was concerned children would end up in "prefabs on the back field".

Phillipstown School is proposed to merge at Woolston School and the ministry expects five additional classrooms will be required to accommodate the merger. "We have to ask the question ‘are they prepared for this?' " Simpson said.

Principals have also asked if the necessary building can be done in time.

Ministry deputy secretary Katrina Casey said there were already unused classrooms at schools in greater Christchurch and where necessary those would be relocated to accommodate the closures and mergers while new facilities were being built.

"No child will be put into accommodation that is of a lesser standard than they currently have if these proposals proceed," Casey said.

The ministry is proposing three schools slated to merge remain on their sites while building work is done at the other school.

In some cases that could be more than two years.

Burwood School is to merge with Windsor School next year, but Burwood will stay on its site until mid-2016.

"This helps to ensure that access to quality education for children and young people is not compromised," Casey said.